Long-lasting second stage of recognition memory consolidation in mice

We investigated the effects of anisomycin (ANI) treatment (150 mg/kg s.c.) during late stages of memory consolidation in a juvenile recognition task in mice. ANI treatment blocked 24 h recognition memory if administered 9 h, 12 h or 15 h after learning. As shown by a significantly reduced incorporation of radioactively labelled amino acids into newly synthesized proteins, translational arrest by ANI treatment lasted for 3-4 h, thus covering the complete time period between 9 h and 18 h after memory acquisition. Together with previous findings [Richter K, Wolf G, Engelmann M. Social recognition memory requires two stages of protein synthesis in mice. Learn Mem 2005;12(4):407-13], our data suggest two distinct stages of protein synthesis to occur during the first 24 h after learning: an early, relatively short-stage, starting immediately after learning and lasting for approximately 3 h, and a second stage starting 6 h after learning lasting for approximately 12 h. This is the first report of such a long-lasting protein synthesis-dependent second consolidation phase in mice and suggests that long-term consolidation of juvenile recognition memory comprises multiple waves of protein synthesis and complex cascades of inter- and intra-cellular signaling processes.